KLB Smear test is used to measure the level of monochromatic granules in the throat swab, This test is performed to detect Corynebacterium infection, Nasopharyyngeal lesions and Skin lesions. Corynebacterium causes diphtheria which is a serious bacterial infection usually affecting the mucous membranes of your nose and throat. Diphtheria typically causes a sore throat, fever, swollen glands and weakness. But the hallmark sign is a sheet of thick, gray material covering the back of your throat, which can block your airway, causing you to struggle for breath.